Method for performing a HARQ process and apparatus using same

ABSTRACT

The present description relates to a method for performing a HARQ process operation in a wireless communication system and to an apparatus using the method. A base station device which performs a HARQ process operation comprises a transmitter which transmits to a relay an uplink (UL) grant in a downlink backhaul subframe n which is a subframe having an index n among the allocated downlink backhaul subframes, and transmits, if downlink data sent from the relay in accordance with the uplink grant is not successfully received, a non-acknowledgement (NACK) signal in a downlink backhaul subframe n+N which is a downlink backhaul subframe that comes after N which is a predetermined number of HARQ processes counted from the downlink backhaul subframe n among the allocated downlink backhaul subframes.

CROSS REFERENCE TO RELATED APPLICATIONS

This non-provisional application is a National Stage entry under U.S.C.§371 of International Application No. PCT/KR2011/004244 filed on Jun. 9,2011, which claims the benefit of U.S. Provisional Application Nos.61/353,209 filed on Jun. 9, 2010, 61/373,267 filed on Aug. 12, 2010,61/377,102 filed on Aug. 26, 2010, 61/381,062 filed on Sep. 8, 2010,61/381,421 filed on Sep. 9, 2010, 61/390,587 filed on Oct. 6, 2010,61/392,027 filed on Oct. 11, 2010, 61/392,934 filed on Oct. 13, 2010,61/411,445 filed on Nov. 8, 2010, and to Korean Patent Application No.10-2011-0055687 filed in Republic of Korea, on Jun. 9, 2011. The entirecontents of all of the above applications are hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates to wireless communication and morespecifically, to a method for performing a HARQ process and an apparatususing the same.

BACKGROUND ART

In wireless communication systems, it is difficult to transmit datasince various types of errors are generated due to propagation oftransmitted signals in a wireless manner. In addition to thermal noiserepresented as additive white Gaussian noise (AWGN), path loss thatincreases with increasing distance from an eNode B (eNB), multi-pathfading, etc. generated in radio channels make reliable signaltransmission difficult.

To secure transmission reliability against generation of various channelstate variations and errors in wireless communication, technologies suchas 1) forward error correction (FEC) or channel coding and 2) automaticrepeat request (ARQ) or hybrid automatic repeat request (HARQ) arewidely used.

In a next-generation 3GPP LTE-A communication system, two types of linkshaving different attributes are respectively applied to uplink anddownlink carrier frequency bands as a relay forwards link connectionbetween en eNB and a user equipment (UE). Connection link establishedbetween the eNB and the relay is defined as a backhaul link. The relaycan receive information from the eNB through a relay backhaul downlinkand transmit information to the eNB through a relay backhaul uplink.Furthermore, the relay can transmit information to the UE through arelay access downlink and receive information from the UE through arelay access uplink.

For the 3GPP LTE-A system to which the relay has been introduced, thereis not provided a HARQ process performed between the relay and the eNBand between the eNB and the UE, for example, a method of determining thenumber of HARQ processes, information about a subframe to which a HARQprocess is applied, etc. Accordingly, a HARQ process taking introductionof a relay into account is needed.

DISCLOSURE Technical Problem

An object of the present invention is to provide a method for performinga HARQ process by an eNB.

Another object of the present invention is to provide a method forperforming a HARQ process by a relay.

Another object of the present invention is to provide an eNB thatperforms a HARQ process.

Another object of the present invention is to provide a relay thatperforms a HARQ process.

The technical problems solved by the present invention are not limitedto the above technical problems and those skilled in the art mayunderstand other technical problems from the following description.

Technical Solution

According to one aspect of the present invention, a method forperforming a HARQ process operation by an eNB in a wirelesscommunication system includes: transmitting, to a relay node, an uplink(UL) grant in a downlink backhaul subframe n which is a subframe havingan index n among allocated downlink backhaul subframes; andtransmitting, if uplink data sent from the relay node in accordance withthe uplink grant is not successfully received, anegative-acknowledgement (NACK) signal in a downlink backhaul subframen+N which is a downlink backhaul subframe that comes after N which is apredetermined number of HARQ processes from the downlink backhaulsubframe n among the allocated downlink backhaul subframes. Thepredetermined number of HARQ processes, N, may be a value determinedaccording to a predefined rule. The predefined rule may be excluding atleast one of a downlink stand-alone subframe, an LTE-A dedicatedsubframe, a fake-multicast broadcast single frequency network (MBSFN)subframe, a non-MBSFN subframe, an almost blank subframe (ABS), apositioning RS subframe, a cell and a true MBSFN subframe from theallocated downlink backhaul subframes in calculation of the number ofHARQ processes.

According another aspect of the present invention, a method forperforming a HARQ process operation by a relay node in a wirelesscommunication system includes: receiving downlink backhaul subframeallocation information from an eNB; transmitting, to the eNB, uplinkdata in a corresponding uplink backhaul subframe on the basis of therelationship between an uplink grant reception time and an uplink datatransmission time, which are predetermined for an uplink grant receivedin a downlink backhaul subframe n; and, if the uplink data is notsuccessfully transmitted, receiving, from the eNB, a NACK signal in adownlink backhaul subframe n+N which is a downlink backhaul subframethat comes after N which is a predetermined number of HARQ processescounted from the downlink backhaul subframe n among the allocateddownlink backhaul subframes, on the basis of the predetermined number ofHARQ processes. The method may further include retransmitting the uplinkdata after a predefined time interval between when the NACK signal isreceived and when the uplink data is retransmitted from the downlinkbackhaul subframe n+N. The predefined time interval may correspond tothree subframes, and the uplink data may be retransmitted in an uplinkbackhaul subframe which comes after three subframes that follow thedownlink backhaul subframe n+N. The downlink backhaul subframeallocation information may include information configured of backhaulsubframes that can be used by the relay node. The method may furtherinclude receiving the NACK signal in the downlink backhaul subframe n+Nwhich is a downlink backhaul subframe that comes after N which is apredetermined number of HARQ processes counted from the downlinkbackhaul subframe n among allocated downlink backhaul subframes otherthan fake-MBSFN subframes from among the backhaul subframes that can beused by the relay node. The downlink backhaul subframe allocationinformation may include the backhaul subframes that can be used by therelay, other than at least one of a downlink stand-alone subframe, anLTE-A dedicated subframe, a fake-MBSFN subframe, a non-MBSFN subframe, apositioning RS subframe, a cell and a true MBSFN subframe. The downlinkbackhaul subframe allocation information may be signaled in a bitmappattern having a predetermine size. The downlink backhaul subframeallocation information may be received through a higher layer signaling.The method may further include receiving the information about thenumber of HARQ processes, N, and the downlink backhaul subframeallocation information and the information about the number of HARQprocesses, N, may be received in the same time period. The method mayfurther include receiving information about backhaul subframes thatcannot be used as downlink backhaul subframes, wherein the NACK signalis received in the downlink backhaul subframe n+N which is a downlinkbackhaul subframe that conies after N which is a predetermined number ofHARQ processes counted from the downlink backhaul subframe n amongdownlink backhaul subframes other than subframes that cannot be used asthe downlink backhaul subframes in the downlink backhaul subframeallocation information.

According to another aspect of the present invention, an eNode B (eNB)apparatus for performing a HARQ process operation in a wirelesscommunication system includes a transmitter configured to transmit, to arelay node, a UL grant in a downlink backhaul subframe n which is asubframe having an index n among allocated downlink backhaul subframesand to transmit, if uplink data sent from the relay in accordance withthe uplink grant is not successfully received, a NACK signal in adownlink backhaul subframe n+N which is a downlink backhaul subframethat comes after N which is a predetermined number of HARQ processesfrom the downlink backhaul subframe n among the allocated downlinkbackhaul subframes.

According to another aspect of the present invention, a relay nodeapparatus for performing a HARQ process operation in a wirelesscommunication system includes: a receiver configured to receive downlinkbackhaul subframe allocation information from an eNB; a transmitterconfigured to transmit, to the eNB, uplink data in a correspondinguplink backhaul subframe on the basis of the relationship between anuplink grant reception time and an uplink data transmission time, whichare predetermined for an uplink grant received in a downlink backhaulsubframe n; and a processor configured to control the receiver toreceive, from the eNB, a NACK signal in a downlink backhaul subframe n+Nwhich is a downlink backhaul subframe that comes after N which is apredetermined number of HARQ processes counted from the downlinkbackhaul subframe n among the allocated downlink backhaul subframes, onthe basis of the predetermined number of HARQ processes, if the uplinkdata is not successfully transmitted.

Advantageous Effects

According to embodiment of the present invention, a HARQ process can beperformed between a relay and an eNB, between the relay and a UE, andbetween the eNB and the UE, and thus communication performance can beimproved through correct HARQ feedback.

The effects of the present invention are not limited to theabove-described effects and other effects which are not described hereinwill become apparent to those skilled in the art from the followingdescription.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a block diagram of a communication system according to anembodiment of the present invention;

FIG. 2 illustrates an exemplary radio frame structure used in a 3GPP LTEsystem corresponding to a mobile communication system;

FIGS. 3 a and 3 b respectively illustrate downlink and uplink subframestructures used in a 3GPP LTE mobile communication system;

FIG. 4 illustrates a time-frequency resource grid structure of downlinkused in the present invention;

FIG. 5 illustrates a configuration of a general MIMO communicationsystem;

FIG. 6 illustrates channels from N_(T) transmit antennas to i receiveantennas;

FIG. 7 illustrates reference signal patterns used in a 3GPP LTE systemcorresponding to a mobile communication system;

FIG. 8 shows an exemplary uplink subframe configuration including an SRSsymbol;

FIG. 9 shows an exemplary frame structure for explaining a HARQ processperformed between a relay and an eNB;

FIG. 10 shows an exemplary frame structure including a downlink grantstand-alone subframe for explaining a HARQ process performed between arelay and an eNB;

FIG. 11 illustrates MBSFN configurations for interference coordination,FIG. 11 a showing interference measurement in a PDSCH region, FIG. 11 bshowing interference measurement in a second slot; and

FIGS. 12 and 13 illustrate exemplary MBSFN subframe configurations.

BEST MODE

Reference will now be made in detail to the preferred embodiments of thepresent invention with reference to the accompanying drawings. Thedetailed description, which will be given below with reference to theaccompanying drawings, is intended to explain exemplary embodiments ofthe present invention, rather than to show the only embodiments that canbe implemented according to the invention. The following detaileddescription includes specific details in order to provide a thoroughunderstanding of the present invention. However, it will be apparent tothose skilled in the art that the present invention may be practicedwithout such specific details. For example, the following detaileddescription is given under the assumption that a mobile communicationsystem is a 3GPP LTE or LTE-A system. However, the description isapplicable to any other mobile communication system except for specificfeatures inherent to 3GPP LTE and LTE-A.

In some instances, known structures and devices are omitted or are shownin block diagram form, focusing on important features of the structuresand devices, so as not to obscure the concept of the invention. The samereference numbers will be used throughout this specification to refer tothe same or like parts.

In the following description, the term terminal generically refers to amobile or fixed user terminal device such as a User Equipment (UE), aMobile Station (MS), an Advanced Mobile Station (AMS), a machine tomachine (M2M) device, etc. In addition, the term Base Station (BS)generically refers to any node at a network end which communicates witha UE, such as a Node B, an evolved Node B (eNB), an Access Point (AP),etc.

In a mobile communication system, a UE can receive information from aneNB on downlink and transmit data to the eNB on uplink. Informationtransmitted from or received at the UE includes data and various typesof control information. There are many physical channels depending onthe types and usages of information transmitted from or received at UEsand eNBs.

FIG. 1 is a block diagram of a communication system according to anembodiment of the present invention.

The communication system according to an embodiment of the invention mayinclude an eNB 100, a relay 150, a UE 180, a network (not shown). WhileFIG. 1 shows one eNB 100, one relay 150 and one UE 180 for simplifyingthe configuration of the communication system, the communication systemcan include a plurality of eNBs, a plurality of relays and a pluralityof UEs.

Referring to FIG. 1, the eNB 100 may include a transmission (Tx) dataprocessor 105, a symbol modulator 110, a transmitter 115, a transceivingantenna 120, a processor 125, a memory 130, a receiver 135, a symboldemodulator 140, and a reception (Rx) data processor 145. The relay 150may include a Tx data processor 155, a symbol modulator 160, atransmitter 165, a transceiving antenna 170, a processor 175, a memory176, a receiver 177, a symbol demodulator 178, and a Rx data processor179. The UE 180 may include a Tx data processor 182, a symbol modulator184, a transmitter 186, a transceiving antenna 188, a processor 190, amemory 192, a receiver 194, a symbol demodulator 196, and a Rx dataprocessor 198.

While FIG. 1 shows that the eNB 100, the relay 150 and the UE 180respectively include the antennas 120, 170 and 188, each of the eNB 100,the relay 150 and the UE 180 includes a plurality of antennas.Accordingly, the eNB 100, the relay 150 and the UE 180 support aMultiple Input Multiple Output (MIMO) system. The eNB 100, the relay 150and the UE 180 according to an embodiment of the present invention cansupport both single user-MIMO (SU-MIMO) and multi-user-MIMO (MU-MIMO).

In downlink, the Tx data processor 105 of the eNB 100 receives trafficdata, formats and codes the received traffic data, and interleaves andmodulates (or symbol-maps) the coded traffic data to generate modulationsymbols (“data symbols”). The symbol modulator 110 receives andprocesses the data symbols and pilot symbols to generate symbol streams.The symbol modulator 110 of the eNB 100 multiplexes the data symbols andthe pilot symbols and transmits the multiplexed symbols to thetransmitter 115. Here, the transmitted symbols may be data symbols,pilot symbols, or null signal values. The pilot symbols may becontiguously transmitted in respective symbol periods. The pilot symbolsmay be frequency division multiplexing (FDM), orthogonal frequencydivision multiplexing (OFDM), time division multiplexing (TDM) or codedivision multiplexing (CDM) symbols. The transmitter 115 of the eNB 100receives the symbol streams, converts the received symbol streams intoone or more analog signals and additionally processes (e.g. amplifies,filters and frequency-upconverts) the analog signals to generate adownlink signal suitable for transmission through a radio channel. Thedownlink signal is transmitted to the relay 150 and/or the UE 180through the antenna 120.

The receive antenna 170 of the relay 150 receives the downlink signalfrom the eNB 100 or receives an uplink signal from the UE 180 andprovides the received signal to the receiver 177. The receiver 177processes (e.g. filters, amplifiers and frequency-downconverts) thereceived signal and digitalizes the processed signal to acquire samples.The symbol demodulator 178 demodulates the received pilot symbols andprovides the demodulated pilot symbols to the processor 175 for channelestimation.

The processor 175 of the relay 150 may demodulate and process thedownlink/uplink signal received from the eNB 100 and/or the UE 180 andtransmit the processed signal to the UE 180 and/or eNB 100 through thetransmit antenna 170.

In the UE 180, the antenna 188 receives a downlink signal from the eNB100 and/or the relay 150 and provides the received signal to thereceiver 194. The receiver 194 processes (e.g. filters, amplifies andfrequency-downconverts) the received signal and digitalizes theprocessed signal to acquire samples. The symbol demodulator 198demodulates received pilot symbols and provides the pilot symbols to theprocessor 190 for channel estimation.

The symbol demodulator 196 receives a frequency response estimationvalue for downlink from the processor 190 and demodulates received datasymbols to obtain data symbol estimation values (estimation values oftransmitted data symbols) and provides the data symbol estimation valuesto the Rx data processor 198. The Rx data processor 150 demodulates thedata symbol estimation values (i.e., performs symbol demapping),deinterleaves and decodes the demodulated data symbol estimation valuesto restore transmitted traffic data.

Processing by the symbol demodulator 196 and the Rx data processor 198is complementary to processing by the symbol modulator 110 and Tx dataprocessor 105 of the eNB 100.

The Tx data processor 182 of the UE 180 processes traffic data toprovide data symbols on uplink. The symbol modulator 184 receives thedata symbols and multiplexes the data symbols with pilot symbols,modulates the multiplexed data symbols and pilot symbols to providesymbol streams to the transmitter 186. The transmitter 186 receives andprocesses the symbol streams to generate an uplink signal. The uplinksignal is transmitted to the eNB 110 or the relay 150 through theantenna 135.

The eNB 100 receives an uplink signal from the UE 180 and/or the relay150 through the antenna 130. The receiver 190 processes the receiveduplink signal to acquire samples. The symbol demodulator 195 processesthe samples to provide pilot symbols and data symbol estimation valuesreceived for uplink. The Rx data processor 197 processes the data symbolestimation values to restore traffic data transmitted from the UE 180and/or the relay 150.

The processors 125, 175 and 190 of the eNB 100, the relay 150 and the UE180 respectively direct (e.g. control, adjust, manage, etc.) operationsof the eNB 100, the relay 150 and the UE 180. The processors 125, 175and 190 may be respectively connected to the memories 130, 176 and 192that store program codes and data. The memories 130, 176 and 192 arerespectively connected to the processors 125, 175 and 190 and storeoperating systems, applications and general files.

The processors 125, 175 and 190 may be referred to as controllers,microcontrollers, microprocessors, microcomputers, etc. The processors125, 175 and 190 may be implemented by hardware, firmware, software or acombination thereof.

When the embodiments of the present invention are implemented usingfirmware or software, the firmware or software may be configured suchthat modules, procedures or functions that perform functions oroperations of the present invention are included in the firmware orsoftware. The firmware or software configured to implement the presentinvention may be included in the processors 125, 175 and 190 or storedin the memories 130, 176 and 192 and executed by the processors 125, 175and 190.

Radio interface protocol layers between the eNB 100, the relay 150 andthe UE 180 and a wireless communication system (network) may beclassified into first layer L1, second layer L2 and third layer L3 onthe basis of lower 3 layers of the open system interconnection (OSI)model well-known in communication systems. A physical layer belongs tofirst layer L1 and provides an information transmission service througha physical channel. A radio resource control (RRC) layer belongs tothird layer L3 and provides control radio resources between the UE 180and the network. The eNB 100, the relay 150 and the UE 180 exchange RRCmessages through the wireless communication network and the RRC layer.

FIG. 2 illustrates an exemplary radio frame structure used in a 3GPP LTEsystem corresponding to a mobile communication system.

Referring to FIG. 2, one radio frame has a length of 10 ms (327200 Ts)and includes ten subframes having an equal size. Each subframe has alength of 1 ms and includes two slots each having a length of 0.5 ms(15360 Ts). Here, Ts denotes a sampling time, which is represented asTx=1/(15 kHz×2048)=3.2552×10⁻⁸ (approximately 33 ns). A slot includes aplurality of Orthogonal Frequency Division Multiplexing (OFDM) symbolsor Single Carrier-Frequency Division Multiple Access (SC-FDMA) symbolsin the time domain and a plurality of resource blocks in the frequencydomain.

In the LTE system, one resource block includes 12 subcarriers×7(6) OFDMsymbols or SC-FDMA symbols. A unit time for transmitting data,Transmission Time Interval (TTI), may be set to one or more subframes.The above-described radio frame structure is exemplary and the number ofsubframes included in the radio frame, the number of slots included inone subframe, and the number of OFDM symbols or SC-FDMA symbols includedin each slot may be changed in various manners.

FIGS. 3 a and 3 b respectively illustrate downlink and uplink subframestructures used in a 3GPP LTE system corresponding to a mobilecommunication system.

Referring to FIG. 3( a), one downlink subframe includes two slots in thetime domain. A maximum of three OFDM symbols located in a front portionof a first slot in the downlink subframe correspond to a control regionallocated with control channels, and the remaining OFDM symbolscorrespond to a data region allocated with a Physical Downlink SharedCHannel (PDSCH).

Examples of downlink control channels used in the 3GPP LTE include aPhysical Control Format Indicator CHannel (PCFICH), a Physical DownlinkControl CHannel (PDCCH), a Physical Hybrid-ARQ Indicator CHannel(PHICH), etc. The PCFICH is transmitted at a first OFDM symbol of asubframe and carries information regarding the number of OFDM symbols(i.e., a control region size) used for transmission of control channelswithin the subframe. Control information transmitted over the PDCCH isreferred to as downlink control information (DCI). The DCI includesuplink resource allocation information, downlink resource allocationinformation, and an uplink transmit power control command for arbitraryuser equipment (UE) groups. The PHICH carries anacknowledgement/not-acknowledgement(ACK/NACK) signal with respect touplink Hybrid Automatic Repeat Request (HARQ). That is, an ACK/NACKsignal with respect to uplink data sent from a UE is transmitted overthe PHICH.

A description will be given of a PDCCH corresponding to a downlinkphysical channel.

The PDCCH can carry a resource allocation and transmission format of aPDSCH (which may be referred to as a DL grant), resource allocationinformation of a PUSCH (which may be referred to as a UL grant), a setof transmit power control commands on individual UEs within an arbitraryUE group, activation of a Voice over Internet Protocol (VoIP), etc. Aplurality of PDCCHs can be transmitted within a control region. A UE canmonitor the PDCCHs. The PDCCH includes an aggregate of one or severalconsecutive Control Channel Elements (CCEs). The PDCCH can betransmitted in the control region after subblock interleaving. A CCE isa logical allocation unit used to provide the PDCCH with a coding ratebased on a state of a radio channel. The CCE corresponds to a pluralityof resource element groups. A format of the PDCCH and the number of bitsof the available PDCCH are determined according to a correlation betweenthe number of CCEs and the coding rate provided by the CCEs.

Control information carried on the PDCCH is called DCI. Table 1 showsDCI according to DCI format.

TABLE 1 DCI Format Description DCI format 0 used for the scheduling ofPUSCH DCI format 1 used for the scheduling of one PDSCH codeword DCIformat 1A used for the compact scheduling of one PDSCH codeword andrandom access procedure initiated by a PDCCH order DCI format 1B usedfor the compact scheduling of one PDSCH codeword with precodinginformation DCI format 1C used for very compact scheduling of one PDSCHcodeword DCI format 1D used for the compact scheduling of one PDSCHcodeword with precoding and power offset information DCI format 2 usedfor scheduling PDSCH to UEs configured in closed- loop spatialmultiplexing mode DCI format 2A used for scheduling PDSCH to UEsconfigured in open-loop spatial multiplexing mode DCI format 3 used forthe transmission of TPC commands for PUCCH and PUSCH with 2-bit poweradjustments DCI format 3A used for the transmission of TPC commands forPUCCH and PUSCH with single bit power adjustments

DCI format 0 conveys uplink resource allocation information, DCI format1 to DCI format 2 are used to indicate downlink resource allocationinformation, and DCI format 3 and DCI format 3A indicate uplink transmitpower control (TPC) command for UE groups.

A method of mapping resources by an eNB for PDCCH transmission in an LTEsystem is described briefly.

In general, the eNB can transmit scheduling allocation information andother control information through a PDCCH. A physical control channelmay be transmitted through an aggregation of one or more contiguousCCEs. A CCE includes 9 resource element groups (REGs). The number ofREGs which are not allocated to a PCFICH or PHICH is represented byNREG. CCEs that can be used in the system correspond to 0 to NCCE-1(here, N_(CCE)=└N_(REG)/9┘). A PDCCH supports multiple formats as shownin the following table 2. A PDCCH composed of n contiguous CCEs startsfrom a CCE that performs i mod n=0 (here, i is a CCE number). MultiplePDCCHs may be transmitted through one subframe.

TABLE 2 Number of PDCCH format Number of CCEs Number of REGs PDCCH bits0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576

Referring to Table 2, the eNB can determine a PDCCH format on the basisof the number of regions in which the eNB will transmit controlinformation. A UE can reduce overhead by reading the control informationon a CCE basis. Similarly, a relay (or relay node) can read the controlinformation on an relay-CCE (R-CCE) basis. In the LTE-A system, resourceelements (REs) can be mapped on an R-CCE basis in order to transmit anR-PDCCH for an arbitrary relay. A description will be given of a methodfor mapping resources to REs when the eNB dynamically allocatesresources in order to transmit R-PDCCHs.

Referring to FIG. 3 b, an uplink subframe can be divided in thefrequency domain into a control region and a data region. The controlregion is allocated with a PUCCH for carrying uplink controlinformation. The data region is allocated with a PUSCH for carrying userdata. To maintain a single carrier property, one UE does notsimultaneously transmit the PUCCH and the PUSCH. The PUCCH for one UE isallocated to an RB pair in a subframe. RBs belonging to the RB pairoccupy different subcarriers in respective two slots. The RB pairallocated to the PUCCH is frequency-hopped in a slot boundary.

FIG. 4 shows a downlink time-frequency resource grid structure used inthe present invention.

A downlink signal transmitted in each slot may be described by aresource grid including N_(RB) ^(DL)×N_(SC) ^(RB) subcarriers andN_(symb) ^(DL) OFDM symbols. N_(RB) ^(DL) indicates the number ofdownlink resource blocks (RBs), N_(SC) ^(RB) represents the number ofsubcarriers which configure one RB, and N_(symb) ^(DL) indicates thenumber of OFDM symbols in one downlink slot. N_(RB) ^(DL) depends on adownlink transmission bandwidth set in a corresponding cell and needs tosatisfy N_(RB) ^(min,DL)≦N_(RB) ^(DL)≦N_(RB) ^(max,DL). Here, N_(RB)^(min,DL) indicates a minimum downlink bandwidth supported by a wirelesscommunication system, and N_(RB) ^(max,RB) represents a maximum downlinkbandwidth supported by the wireless communication system. While N_(RB)^(min,DL) may be 6 and N_(RB) ^(max,RB) may be 110, they are not limitedthereto. The number of OFDM symbols included in one slot may depend onthe length of Cyclic Prefix (CP) and a subcarrier interval. In case ofmulti-antenna transmission, one resource grid can be defined per antennaport.

An element in the resource grid for each antenna port is called aResource Element (RE) and uniquely identified by an index pair (k, l) ina slot. Here, k indicates a frequency-domain index ranging from 0 toN_(RB) ^(DL)N_(SC) ^(RB)−1, and l indicates a time-domain index rangingfrom 0 to N_(symb) ^(DL)−1.

A RB shown in FIG. 4 is used to describe the mapping relationshipbetween a physical channel and REs. RBs may be classified into aphysical RB (PRB) and a virtual RB (VRB). One PRB is defined as N_(symb)^(DL) consecutive OFDM symbols in the time domain and N_(SC) ^(RB)consecutive subcarriers in the frequency domain. Here, N_(symb) ^(DL)and N_(SC) ^(RB) may be predetermined values. For example, N_(symb)^(DL) and N_(SC) ^(RB) may have values as shown in the following Table3. Accordingly, one PRB includes N_(symb) ^(DL)×N_(SC) ^(RB) REs. Whileone PRB can correspond to one slot in the time domain and correspond to180 kHz in the frequency domain, it is not limited thereto.

TABLE 3 Configuration N_(sc) ^(RB) N_(symb) ^(DL) Normal Δf = 15 kHz 127 cyclic prefix Extended Δf = 15 kHz 6 cyclic Δf = 7.5 kHz 24 3 prefix

One PRB has a value in the range of 0 to N_(RB) ^(DL)−1 in the frequencydomain. The relationship between a PRB number n_(PRB) in the frequencydomain and a resource element (k, l) in one slot satisfies

$n_{PRB} = {\left\lfloor \frac{k}{N_{sc}^{RB}} \right\rfloor.}$

The VRB has a size equal to the PRB. The VRB can be classified into alocalized VRB (LVRB) and a distributed VRB (DVRB). For each VRB type, apair of VRBs in two slots of one subframe are allocated with a singleVRB number n_(VRB).

The VRB may have a size equal to the PRB. For each of the LVRB and DVRB,a pair of VRB having a single VRB index (which may be referred to as aVRB number) are allocated to two slots in one subframe. In other words,N_(RB) ^(DL) VRBs which belong to the first one of two slots in onesubframe are allocated with one of indexes in the range of 0 to N_(RB)^(DL)−1, and N_(RB) ^(DL) VRBs which belong to the second slot are alsoallocated with one of the indexes in the range of 0 to N_(RB) ^(DL)−1.

A description will be given of a general multiple input multiple output(MIMO) scheme. MIMO can improve transmission/reception data efficiencyusing multiple transmit antennas and multiple receive antennas. That is,MIMI uses multiple antennas at a transmitter or receiver of a wirelesscommunication system to improve capacity or performance. MIMO isreferred to as “multi-antenna” hereinafter.

A multi-antenna technology collects data pieces received throughmultiple antennas and combines the received data pieces to accomplish awhole message without depending on a single antenna path. Accordingly,it is possible to increase a data transmission rate in a specific rangeor improve a system range for a specific data transmission rate.

Since next-generation mobile communication requires a data transmissionrate much higher than that of conventional mobile communication, it isexpected that an efficient multi-antenna technology is needed. MIMOattracts people's attention as a next-generation mobile communicationtechnology which can be widely used for mobile communication terminalsand relays and can overcome transmission capacity limit of mobilecommunication due to extension of data communication.

Among various technologies for improving transmission efficiency underdevelopment, MIMO using multiple antennas at a transmitter and areceiver can remarkably improve communication capacity andtransmission/reception performance without allocating an additionalfrequency or increasing power.

FIG. 5 shows the configuration of a general MIMO communication system.

As shown in FIG. 5, when the number of transmit antennas and the numberof receive antennas are increased to N_(T) and N_(R) respectively, achannel transmission capacity increases in proportion to the number ofantennas in theory, distinguished from a case in which only transmitteror receiver uses multiple antennas. Accordingly, a transmission rate andfrequency efficiency can be improved. The transmission rate can beincreased by the product of a maximum transmission rate R₀ when a singleantenna is used and a rate of increase R_(i) represented by Equation 1according to increase in the channel transmission capacitytheoretically.R _(i)=min(N _(T) ,N _(R))  [Equation 1]

A communication scheme in the MIMO system will be described below usinga mathematical model.

It is assumed that there are N_(T) transmit antennas and N_(R) receiveantennas in the MIMO system, as shown in FIG. 5.

Regarding a transmission signal, up to N_(T) pieces of information canbe transmitted through the N_(T) transmit antennas, as expressed as thefollowing vector.s=[s ₁ , s ₂ , . . . , s _(N) _(T) ]^(T)  [Equation 2]

A different transmit power may be applied to each piece of transmissioninformation s₁, s₂, . . . , s_(N) _(T) . Let the transmit power levelsof the transmission information be denoted by P₁, P₂, . . . , P_(N) _(T), respectively. Then the transmit power-controlled transmissioninformation ŝ may be given as [Equation 3].ŝ=[ŝ ₁ , ŝ ₂ , . . . , ŝ _(N) _(T) ]^(T) =[P ₁ s ₁ , P ₂ s ₂ , . . . , P_(N) _(T) s _(N) _(T) ]^(T)  [Equation 3]

ŝ may be expressed as a diagonal matrix P of transmit power.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Let's consider a case in which actual N_(T) transmitted signals x₁, x₂,. . . , x_(N) _(T) are configured by applying a weight matrix W to thetransmit power-controlled information vector ŝ. The weight matrix Wfunctions to appropriately distribute the transmission information tothe antennas according to transmission channel statuses, etc. Thesetransmitted signals x₁, x₂, . . . , x_(N) _(T) are represented as avector X, which may be determined as

$\begin{matrix}\begin{matrix}{X = \begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{bmatrix}} \\{= {\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1N_{T}} \\w_{21} & w_{22} & \ldots & w_{2N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 1} & w_{i\; 2} & \ldots & w_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \ldots & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\\vdots \\{\hat{s}}_{j} \\\vdots \\{\hat{s}}_{N_{T}}\end{bmatrix}}} \\{= {W\hat{s}}} \\{= {WPs}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

In Equation 5, w_(ij) denotes a weight for a j^(th) piece of informationŝ_(j) transmitted through an i^(th) transmit antenna. W is also referredto as a weight matrix or a precoding matrix.

The transmitted signals X may be considered in a case using spatialdiversity and a case using spatial multiplexing.

Elements of the information vector s have different values sincedifferent signals are multiplexed and transmitted in the case usingspatial multiplexing, whereas all the elements of the information vectors have the same value since the same signal is transmitted throughmultiple channel paths when spatial diversity is used.

A method of combining spatial multiplexing and spatial diversity mayalso be considered. For example, the same signal can be transmittedthrough three transmit antennas using spatial diversity and othersignals can be spatially multiplexed and transmitted. Given N_(R)receive antennas, signals received at the receive antennas, y₁, y₂, . .. , y_(N) _(R) may be represented as the following vector.y=[y ₁ , y ₂ , . . . , y _(N) _(R) ]^(T)  [Equation 6]

When channels are modeled in the MIMO wireless communication system,they may be distinguished according to the indexes of the transmitantennas and receive antennas. A channel between a j^(th) transmitantenna and an i^(th) receive antenna is represented as h_(ij). It is tobe noted herein that the index of the receive antenna precedes that ofthe transmit antenna in h_(ij). A plurality of channels may be combinedand represented by a vector and matrix. An example of vectorrepresentation will now be described.

FIG. 6 illustrates channels from N_(T) transmit antennas to an i^(th)receive antenna.

Referring to FIG. 6, the channels from the N_(T) transmit antennas tothe i^(th) receive antenna may be expressed as [Equation 7].h _(i) ^(T) =[h _(i1) , h _(i2) , . . . , h _(iN) _(T) ]  [Equation 7]

Hence, all channels from the N_(T) transmit antennas to the N_(R)receive antennas may be expressed as the following matrix.

$\begin{matrix}{H = {\begin{bmatrix}h_{1}^{T} \\h_{2}^{T} \\\vdots \\h_{i}^{T} \\\vdots \\h_{N_{R}}^{T}\end{bmatrix} = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

Actual channels experience the above channel matrix H and then are addedwith Additive White Gaussian Noise (AWGN). The AWGN n₁, n₂, . . . ,n_(N) _(R) added to the N_(R) receive antennas is given as the followingvector.n=[n ₁ , n ₂ , . . . , n _(N) _(R) ]^(T)  [Equation 9]

From the above modeled equations, the received signal is given as

$\begin{matrix}\begin{matrix}{y = \begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{i} \\\vdots \\y_{N_{R}}\end{bmatrix}} \\{= {{\begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{j} \\\vdots \\x_{N_{T}}\end{bmatrix}} + \begin{bmatrix}n_{1} \\n_{2} \\\vdots \\n_{i} \\\vdots \\n_{N_{R}}\end{bmatrix}}} \\{= {{Hx} + n}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$

The number of columns and rows of a channel matrix H which indicates achannel state is determined by the number of transmit and receiveantennas. The number of columns in the channel matrix H equals to thenumber of receive antennas, N_(R), and the number of rows equals to thenumber of transmit antennas, N_(T). That is, the channel matrix Hcorresponds to N_(R)×N_(T).

The rank of a matrix is defined as the minimum of the numbers ofindependent rows or columns. Accordingly, the rank of the matrix is notlarger than the number of rows or columns. The rank of the channelmatrix H, rank(H) is limited as follows.rank(H)≦min(N _(T) ,N _(R))  [Equation 11]

In a mobile communication system, a packet (or signal) is transmitted ona radio channel from a transmitter to a receiver. In view of the natureof the radio channel, the packet may be distorted during thetransmission. To receive the signal successfully, the receiver shouldcompensate for the distortion in the received signal using channelinformation. Generally, to enable the receiver to acquire the channelinformation, the transmitter transmits a signal known to both thetransmitter and the receiver and the receiver acquires knowledge ofchannel information based on the distortion of the signal received onthe radio channel. This signal is called a pilot signal or a referencesignal.

In the conventional system, the transmitter transmits a packet to thereceiver using one transmit antenna and one receive antenna. Mostcurrent mobile communication systems adopt multiple transmit antennasand multiple receive antennas to improve transmission/reception dataefficiency. In case of data transmission and reception through multipleantennas in a mobile communication system for the purpose of improvingcapacity and communication performance, a reference signal existsseparately for each transmit antenna. The receiver can successfullyreceive a signal transmitted from each transmit antenna using a knownreference signal for each transmit antenna.

In a mobile communication system, RSs may be divided into an RS forchannel information acquisition and an RS for data demodulation. Theformer needs to be transmitted over a broadband because it is foracquiring downlink channel information of a UE and to be received andmeasured by a UE even if the UE does not receive downlink data in aspecific subframe. This RS for channel measurement can be used formeasurement of handover. The latter is transmitted with a correspondingresource when an eNB sends a downlink signal. A UE receives this RS toperform channel estimation and demodulate data. This RS for demodulationneeds to be transmitted in a data transmission region.

FIG. 7 illustrates reference signal patterns used in a 3GPP LTE systemcorresponding to a mobile communication system. FIG. 7( a) shows an RSpattern in a normal CP case and FIG. 7( b) shows an RS pattern in anextended CP case.

In a 3GPP LTE release-8 system, two types of downlink RSs are definedfor unicast service. That is, there are a common reference signal (CRS)used for channel state information acquisition and handover measurementand a dedicated reference signal (DRS) (corresponding to UE-specific RS)used for data demodulation. In LTE release-8 system, the UE-specific RSis used only for data demodulation, whereas the CRS is used for channelinformation acquisition and data demodulation. The CRS is acell-specific RS, and an eNB transmits a CRS for each subframe over awideband. Cell-specific CRSs are transmitted for up to four antennaports according to the number of transmit antennas of the eNB.

AS shown in FIGS. 7( a) and 7(b), CRSs 1, 2, 3 and 4 (respectivelyindicating reference signals R0, R1, R2 and R3 for four antenna ports)for four antenna ports are allocated to time-frequency resources in oneRB such that the time-frequency resources do not overlap. When CRSs aremapped to time-frequency resources in an LTE system, an RS for oneantenna port is mapped to one RE per six REs and transmitted in thefrequency domain. Since one RB includes 12 REs in the frequency domain,two REs per RB are used for one antenna port.

As shown in FIGS. 7( a) and 7(b), a DRS (denoted by “D”) is used forsingle-antenna port transmission of a PDSCH. A UE can receiveinformation representing presence or absence of a UE-specific RS from ahigher layer. If data demodulation is needed, the UE-specific RS istransmitted to the UE through an RE. RS mapping rules for mapping an RSto a resource block may be expressed as [Equation 12] to [Equation 14].[Equation 12] represents a CRS mapping rule, [Equation 13] represents aDRS mapping rule to which the normal CP is applied, and [Equation 14]expresses a DRS mapping rule to which the extended CP is applied.

$\begin{matrix}{{k = {{6m} + {\left( {v + v_{shift}} \right){mod}\; 6}}}{l = \left\{ {{{\begin{matrix}{0,{N_{symb}^{DL} - 3}} & {{{if}\mspace{14mu} p} \in \left\{ {0,1} \right\}} \\1 & {{{if}\mspace{14mu} p} \in \left\{ {2,3} \right\}}\end{matrix}m} = 0},1,\ldots\mspace{20mu},{{{2 \cdot N_{RB}^{DL}} - {1m^{\prime}}} = {{m + N_{RB}^{\max,{DL}} - {N_{RB}^{DL}v}} = \left\{ {{\begin{matrix}0 & {{{if}\mspace{14mu} p} = {{0\mspace{14mu}{and}\mspace{14mu} l} = 0}} \\3 & {{{if}\mspace{14mu} p} = {{0\mspace{14mu}{and}\mspace{14mu} l} \neq 0}} \\3 & {{{if}\mspace{14mu} p} = {{1\mspace{14mu}{and}\mspace{14mu} l} = 0}} \\0 & {{{if}\mspace{14mu} p} = {{1\mspace{14mu}{and}\mspace{14mu} l} \neq 0}} \\{3\left( {n_{s}\mspace{14mu}{mod}\mspace{20mu} 2} \right)} & {{{if}\mspace{14mu} p} = 2} \\{3 + {3\left( {n_{s}\mspace{20mu}{mod}\mspace{20mu} 2} \right)}} & {{{if}\mspace{14mu} p} = 3}\end{matrix}v_{shift}} = {N_{ID}^{cell}\mspace{14mu}{mod}\mspace{20mu} 6}} \right.}}} \right.}} & \left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack \\{{k = {{\left( k^{\prime} \right)\mspace{14mu}{mod}\mspace{14mu} N_{sc}^{RB}} + {N_{sc}^{RB} \cdot n_{PRB}}}}{k^{\prime} = \left\{ {{\begin{matrix}{{4m^{\prime}} + v_{shift}} & {{{if}\mspace{14mu} l} \in \left\{ {2,3} \right\}} \\{{4m^{\prime}} + {\left( {2 + v_{shift}} \right)\mspace{14mu}{mod}\mspace{20mu} 4}} & {{{if}\mspace{14mu} l} \in \left\{ {5,6} \right\}}\end{matrix}l} = \left\{ {{\begin{matrix}3 & {l^{\prime} = 0} \\6 & {l^{\prime} = 1} \\2 & {l^{\prime} = 2} \\5 & {l^{\prime} = 3}\end{matrix}l^{\prime}} = \left\{ {{{\begin{matrix}{0,1} & {{{if}\mspace{14mu} n_{s\mspace{14mu}}{mod}{\mspace{14mu}\;}2} = 0} \\{2,3} & {{{if}\mspace{14mu} n_{s\mspace{14mu}}{mod}\mspace{20mu} 2} = 1}\end{matrix}m^{\prime}} = 0},1,\ldots\mspace{14mu},{{{3N_{RB}^{PDSCH}} - {1v_{shfit}}} = {N_{ID}^{cell}\mspace{14mu}{mod}{\mspace{14mu}\;}3}}} \right.} \right.} \right.}} & \left\lbrack {{Equation}\mspace{14mu} 13} \right\rbrack \\{{k = {{\left( k^{\prime} \right)\mspace{14mu}{mod}\mspace{14mu} N_{sc}^{RB}} + {N_{sc}^{RB} \cdot n_{PRB}}}}{k^{\prime} = \left\{ {{\begin{matrix}{{3m^{\prime}} + v_{shift}} & {{{if}\mspace{14mu} l} = 4} \\{{3m^{\prime}} + {\left( {2 + v_{shift}} \right)\mspace{14mu}{mod}\mspace{20mu} 3}} & {{{if}\mspace{14mu} l} = 1}\end{matrix}l} = \left\{ {{\begin{matrix}4 & {l^{\prime} \in \left\{ {0,2} \right\}} \\1 & {l^{\prime} = 1}\end{matrix}l^{\prime}} = \left\{ {{{\begin{matrix}0 & {{{if}\mspace{14mu} n_{s\mspace{14mu}}{mod}\mspace{20mu} 2} = 0} \\{1,2} & {{{if}\mspace{14mu} n_{s}\mspace{14mu}{mod}\mspace{20mu} 2} = 1}\end{matrix}m^{\prime}} = 0},1,\ldots\mspace{14mu},{{{4N_{RB}^{PDSCH}} - {1v_{shfit}}} = {N_{ID}^{cell}\mspace{14mu}{mod}{\mspace{14mu}\;}3}}} \right.} \right.} \right.}} & \left\lbrack {{Equation}\mspace{14mu} 14} \right\rbrack\end{matrix}$

In [Equation 12] to [Equation 14], k and p respectively denote asubcarrier index and an antenna port, and N_(RB) ^(DL), n_(s) andN_(cell) ^(ID) respectively represent the number of RBs, the number ofslot indexes and the number of cell IDs, allocated to downlink. Theposition of an RS depends on V_(shift) in the frequency domain.

3GPP LTE-A is expected to support coordinated multi-point (CoMP) andmulti-user-MIMO (MU-MIM) that are not supported by the conventionalsystems to improve a data transmission rate. CoMP refers to a system inwhich two or more eNBs or cells in cooperation with each othercommunicate with UEs to improve communication performance between a UEand an eNB (cell or sector) in a shaded area.

CoMP may be divided into CoMP-Joint Processing (CoMP-JP) in the form ofcoordinate MIMO through data sharing and CoMP-coordinatedscheduling/beamforming (CoMP-CS/CB).

In case of downlink, a UE can simultaneously receive data from eNBs thatperform CoMP and combine signals received from the eNBs to improvereception performance in the CoMP-JP scheme. In the CoMP-CS, the UE caninstantaneously receive data from one eNB through beamforming.

In case of uplink, each eNB can simultaneously receive PUSCH signalsfrom UEs in the CoMP-JP scheme. In the CoMP-CS scheme, only one eNBreceives a PUSCH. Here, use of CoMP-CS is determined by coordinatedcells (or eNBs).

In MU-MIMO, an eNB allocates antenna resources to UEs. That is, Mu-MIMOselects and schedules UEs capable of transmitting data at a high datatransmission rate for each antenna. MU-MIMO improves system throughput.

FIG. 8 shows an exemplary uplink subframe configuration including an SRSsymbol.

Referring to FIG. 8, a sounding reference signal (SRS) is used for aneNB to measure channel quality and perform uplink frequency-selectivescheduling based on the channel quality measurement. The SRS is notassociated with uplink data and/or control information transmission.However, the SRS may also be used for enhanced power control or forproviding various functions for non-scheduled UEs. The SRS used foruplink channel measurement and as a pilot signal transmitted from a UEto an eNB is used for the eNB to estimate the state of a channel fromeach UE to the eNB. Channels on which the SRS is transmitted may havedifferent transmission bandwidths and transmission intervals for UEsaccording to UE states. The eNB can determine a UE whose data channel isscheduled on the basis of a channel estimation result.

The SRS may be used for measuring downlink channel quality on theassumption of the reciprocity of a radio channel between the downlinkand the uplink. This assumption is valid especially in a time divisionduplex (TDD) system in which downlink and uplink share the samefrequency band and are distinguished by time. A subframe in which a UEwithin a cell is supposed to transmit an SRS is indicated bycell-specific broadcast signaling. A 4-bit cell-specific parameter‘srsSubframeConfiguration’ indicates 15 possible sets of subframescarrying SRSs in each radio frame. This configuration may provideflexibility with which SRS overhead can be adjusted. An SRS may betransmitted in the last SC-FDMA symbol of a configured subframe.

Therefore, an SRS and a DMRS are positioned in different SC-FDMA symbolsin a subframe. SRSs of UEs, transmitted in the last SC-FDMA symbols ofthe same subframe, may be distinguished by frequency positions thereof.PUSCH data transmission is not allowed in an SC-FDMA symbol designatedfor SRS transmission. Accordingly, even the highest sounding overhead(in the case where SRS symbols exist in all subframes) does not exceed7%.

Each SRS symbol is generated using a constant amplitude zero autocorrelation (CAZAC) sequence. SRSs transmitted from a plurality of UEsare CAZAC sequences, r^(SRS)(n)=r_(u,v) ^((α))(n) having differentcyclic shift values according to [Equation 15]. Here, r^(SRS)(n)represents an SRS sequence.

$\begin{matrix}{\alpha = {2\pi\frac{n_{SRS}^{cs}}{8}}} & \left\lbrack {{Equation}\mspace{14mu} 15} \right\rbrack\end{matrix}$

Here, n_(SRS) ^(cs) is a value set for each UE by a higher layer and isan integer in a range of 0 to 9. CAZAC sequences generated from oneCAZAC sequence through cyclic shift have zero-correlation with sequenceshaving cyclic shift values different those thereof. By using thischaracteristic, SRSs in the same frequency region can be distinguishedby CAZAC sequence cyclic shift value. An SRS of each UE is allocated inthe frequency domain according to a parameter set by the eNB. A UEperforms frequency hopping of an SRS such that the SRS can betransmitted over the entire data transmission bandwidth.

A description will be given of relay types. In relation to the use of abandwidth (or spectrum) of a relay, the case where a backhaul linkoperates in the same frequency band as an access link is referred to asin-band, and the case where the backhaul link operates in differentfrequency bands from the access link is referred to as out-band. In boththe in-band and the out-band, UEs operating according to the existingLTE system (e.g., Release-8) should be able to access a donor cell.

The relay may be classified into a transparent relay and anon-transparent relay depending on whether or not the UE recognizes therelay. In the transparent relay, the UE is not aware that it iscommunicating with a network via the relay, and in the non-transparentrelay, the UE is aware that it is communicating with the network via therelay.

In relation to control of the relay, the relay may be divided into arelay as part of a donor cell and a relay for controlling a cell of itsown.

The relay as part of the donor cell may have a relay ID but does nothave a cell ID of its own. If at least part of Radio Resource Management(RRM) is controlled by an eNB to which the donor cell belongs (whileparts of the RRM may be located in the relay), this may be called arelay as part of the donor cell. Desirably, such a relay may supportlegacy UEs. Smart repeaters, decode-and-forward relays, different typesof L2 (second layer) relays, and type-2 relays are examples of this typeof relay.

In the case where a relay is in control of its own cells, the relaycontrols one or several cells and a unique physical-layer cell ID isprovided to each of the cells controlled by the relay. The same RRMmechanism is available and in terms of the UE there is no difference inaccessing cells controlled by a relay and cells controlled by a normaleNB. The cells controlled by the relay may support the legacy UEs.Self-backhauling relays, L3 (third layer) relays, type-1 relays, andtype-1a relays are examples of this type of relay.

A type-1 relay is an in-band relay and controls a plurality of cells,each of which appears as a separate cell, distinct from the donor cell,to UEs. The plurality of cells has its own physical cell ID (defined inLTE Release-8) and the relay may transmit its own synchronizationchannels, reference signals, etc. In the context of single-celloperation, the UE may receive scheduling information and HARQ feedbackdirectly from the relay and may transmit its own control channels (SR,CQI, ACK/NACK, etc.) to the relay. The type-1 relay appears as a legacyeNB (an eNB operating according to LTE Release-8) to legacy UEs (UEsoperating according to LTE Release-8). Namely, the type-1 relay hasbackward compatibility. Meanwhile, to UEs operating according to anLTE-A system, the type-1 relay appears as an eNB different from thelegacy eNB to allow for performance enhancement.

A type-1a relay has the same characteristics as the above-mentionedtype-1 relay except that it operates in out-band. The operation of thetype-1a relay may be configured to minimize an influence on theoperation of an L1 (first layer) or to eliminate such influence.

A type-2 relay, which is an in-band relay, does not have a separatephysical cell ID and thus does not create any new cells. The type-2relay is transparent to the legacy UEs, and the legacy UEs are not awareof the presence of the type-2 relay. The type-2 relay may transmit aPDSCH but does not transmit a Common Reference Signal (CRS) and a PDCCH.

Meanwhile, in order to allow in-band operation of the relay, someresources in the time-frequency space should be reserved for thebackhaul link and may be set not to be used for the access link. This iscalled resource partitioning.

A general principle for resource partitioning in the relay is asfollows. The backhaul downlink and access downlink may be time divisionmultiplexed in a single carrier frequency (namely, only one of thebackhaul downlink and access downlink is activated at a specific time).Similarly, the backhaul uplink and access uplink may be time divisionmultiplexed in a single carrier frequency (namely, only one of thebackhaul uplink and access uplink is activated at a specific time).

In multiplexing the backhaul links for FDD, backhaul downlinktransmission and backhaul uplink transmission are carried out in adownlink frequency band and an uplink frequency band, respectively. Inmultiplexing the backhaul links for TDD, backhaul downlink transmissionand backhaul uplink transmission are carried out in downlink subframesof the eNB and relay and uplink subframes of the eNB and relay,respectively.

In the case of an in-band relay, for example, if reception of thebackhaul downlink from the eNB and transmission of the access downlinkto the UE are simultaneously performed in a predetermined frequencyband, a signal transmitted from a transmitting end of the relay may bereceived in a receiving end of the relay and thus signal interference orRadio Frequency (RF) jamming may occur at an RF front end of the relay.Similarly, if reception of the access uplink from the UE andtransmission of the backhaul uplink to the eNB are simultaneouslyperformed in a predetermined frequency band, signal interference mayoccur at the RF front end of the relay. Accordingly, in the relay,simultaneous transmission and reception in a single frequency band isdifficult to achieve unless sufficient separation between a transmissionsignal and a reception signal is provided (e.g., unless a transmissionantenna and a reception antenna are sufficiently separated from eachother geographically (for example, by installing them above/belowground)).

One method for solving the problem of signal interference is to allowthe relay not to transmit a signal to UEs while receiving a signal fromthe donor cell. That is, a gap may be generated in transmission to theUEs from the relay and the UEs (including the legacy UEs) may be set notto expect any transmission from the relay during the gap. Such a gap maybe set by configuring a Multicast Broadcast Single Frequency Network(MBSFN) subframe.

In the present description, a subframe corresponding to the backhaullink between the eNB and the relay is referred to as a Un subframe and asubframe corresponding to the access link between the relay and the UEis referred to as an access subframe or a Uu subframe. However, thepresent invention is not limited thereto.

A description will be given of a method of signaling the number ofHybrid Automatic Repeat request (HARQ) processes and a method ofdetermining the number of HARQ processes according to embodiments of thepresent invention. The method of signaling the number of HARQ processesby the eNB is described first. The method of determining the number ofHARQ processes and the method of signaling the number of HARQ processescan also be applied to the UE as well as the relay. That is, thesemethods can be applied to a HARQ process between the eNB and the UE withthe introduction of an advanced PDCCH as an enhancement version of thePDCCH to the LTE-A system. A HARQ process performed between the relayand the eNB, which is introduced to the LTE-A system, is described inmore detail.

The number of HARQ processes needs to be calculated on the basis ofavailable backhaul subframes other than subframes that cannot be used asbackhaul subframes (e.g. backhaul subframes that cannot configure MBSFNsubframes). The number of HARQ processes may be signaled by the eNBthrough RRC signaling or directly calculated by the relay or the UE.Otherwise, the eNB, relay and UE may share information about the numberof HARQ processes by previously defining the number of HARQ processesand a bitmap that indicates available backhaul subframes correspondingto the number of HARQ processes, as shown in Table 4.

TABLE 4 Number of uplink HARQ Decimal equivalent ofSubframeConfigurationFDD processes 1, 2, 4, 8, 16, 32, 64, 128 1 3, 5,6, 9, 10, 12, 17, 18, 20, 24, 33, 34, 36, 40, 48, 65, 2 66, 68, 72, 80,96, 129, 130, 132, 136, 144, 160, 192 7, 11, 13, 14, 19, 21, 22, 25, 26,28, 35, 37, 38, 41, 42, 3 44, 49, 50, 52, 56, 67, 69, 70, 73, 74, 76,81, 82, 84, 85, 88, 97, 98, 100, 104, 112, 131, 133, 134, 137, 138, 140,145, 146, 148, 152, 161, 162, 164, 168, 170, 176, 193, 194, 196, 200,208, 224 15, 23, 27, 29, 30, 39, 43, 45, 46, 51, 53, 54, 57, 58, 4 60,71, 75, 77, 78, 83, 86, 87, 89, 90, 91, 92, 93, 99, 101, 102, 105, 106,107, 108, 109, 113, 114, 116, 117, 120, 135, 139, 141, 142, 147, 149,150, 153, 154, 156, 163, 165, 166, 169, 171, 172, 173, 174, 177, 178,180, 181, 182, 184, 186, 195, 197, 198, 201, 202, 204, 209, 210, 212,213, 214, 216, 218, 225, 226, 228, 232, 234, 240 31, 47, 55, 59, 61, 62,79, 94, 95, 103, 110, 111, 115, 5 118, 119, 121, 122, 123, 124, 125,143, 151, 155, 157, 158, 167, 175, 179, 183, 185, 187, 188, 189, 190,199, 203, 205, 206, 211, 215, 217, 219, 220, 221, 222, 227, 229, 230,233, 235, 236, 237, 238, 241, 242, 244, 245, 246, 248, 250 63, 126, 127,159, 191, 207, 223, 231, 239, 243, 247, 6 249, 251, 252, 253, 254, 255

Referring to Table 4, the number of HARQ processes in the relay isdetermined according to subframes configured for transmission betweenthe eNB and the relay. For example, for FDD frame structure type 1, thenumber of HARQ processes can be determined by a decimal valuecorresponding to a binary number indicating an 8-bit bitmap of parameter‘SubframeConfigurationFDD’. The eNB and the relay may previously shareTable 4. The HARQ processes may be consecutively allocated in thesubframes configured for transmission between the eNB and the relay.

While backhaul subframes that cannot configure MBSFN subframes areexemplified as subframes that cannot be used as backhaul subframes,there are many types of unavailable backhaul subframes, which will bedescribed below.

The eNB signals the number (N) of currently performed HARQ processes tothe relay through higher layer signaling. The relay (relay node) canrecognize a subframe in which uplink data that needs to be retransmittedby the relay has been transmitted using the number (N) of HARQprocesses, received from the eNB through higher layer signaling at aspecific time. According to this method, a round trip time (RTT)necessary for retransmission after initial transmission of the relay isvariable and this variable RTT can be recognized using the number ofactually performed HARQ processes and other information.

In the following description, it is assumed that the relay transmitsuplink data in a subframe (i.e. subframe n+4) having an index of n+4when the number of uplink backhaul subframes equals the number ofdownlink backhaul subframes and the eNB transmits a UL grant in asubframe (i.e. subframe n) having an index of n.

FIG. 9 shows an exemplary frame structure for explaining a HARQ processperformed between the eNB and the relay.

In FIG. 9, shaded portions represent subframes allocated as backhaulsubframes. If the eNB does not successfully receive the uplink data fromthe relay, the relay can detect a downlink subframe in which a downlinkNACK signal with respect to the uplink data is transmitted, using valueN. If N=3 (if the number of HARQ processes is 3) and the NACK signal istransmitted in the third downlink subframe (in the case in whichsubframes are indexed in consideration of only subframes allocated todownlink backhaul resources) from a subframe n in which the UL grant istransmitted, when the eNB transmits the UL grant in the subframe n, therelay transmits the uplink data in the subframe n+4. If the eNB does notreceive the uplink data, the relay needs to retransmit the uplink datathat has been transmitted in uplink subframe n+4. In this case, therelay retransmits the uplink data in a subframe n+14. Here, the uplinkdata is the data that has failed to be initially transmitted in thesubframe n+4 that comes before N (N=3 in the case of FIG. 9) subframes(on the basis of the number of subframes allocated as uplink backhaulsubframes) from the subframe n+14. In the same manner, for downlink, itis assumed that, if the eNB cannot successfully receive the uplink datainitially transmitted from the relay in uplink subframe n+4, a NACKsignal for the uplink data is transmitted to the relay in a backhaulsubframe (i.e. subframe n+10) that comes N (N=3 in the case of FIG. 9)subframes after subframe n.

When the eNB signals the number (N) of HARQ processes to the relaythrough higher layer signaling, the relay can detect a subframecorresponding to a process ID allocated thereto using a very simplemethod. If the eNB does not explicitly signal value N to the relay, theprocessor 175 of the relay estimates value N on the basis of a maximumnumber of downlink subframes present in a minimum HARQ RTT window.However, this method is complicated because it should perform windowsearch for a plurality of subframes.

Since the number (N) of HARQ processes can be used to detect a HARQprocess ID, it may be desirable that the eNB transmit the value N at thesame timing as higher layer signaling (e.g. RRC signaling) used fordownlink backhaul subframe allocation. Furthermore, the eNB may transmitinformation representing the number (N) of HARQ processes by includingthe same in downlink backhaul subframe allocation information.Accordingly, considering that the number of HARQ processes changes onlywhen a downlink/uplink subframe allocation pattern varies, it may bedesirable that the eNB transmit value N and downlink/uplink backhaulsubframe allocation information together to the relay.

Alternatively, the eNB may not signal value N when the downlink/uplinksubframe allocation pattern does not change according to eventtriggering, or may signal that value N does not change using an N-bitfield or an additional bit. The eNB may also signal value N only whenthe downlink/uplink backhaul subframe allocation pattern changes, asdescribed above. When N is transmitted only when the downlink/uplinkbackhaul subframe allocation pattern changes, the eNB may additionallyconfigure signaling information of value N.

For the HARQ process described with respect to FIG. 9, uplink granttransmission timing and uplink data retransmission time can be describedmore clearly by introducing a virtual index in addition to theconventional subframe index to the backhaul link (Un link) between theeNB and the relay. Virtual subframe indexes (virtual indexes) aresequentially allocated only to subframes assigned to the Un link(backhaul link). The virtual subframe indexes are defined only for a ULgrant and uplink/downlink paired subframes which are paired duringtransmission even when a downlink stand-alone subframe exists. That is,the virtual subframe index is not defined for the downlink stand-alonesubframe. Accordingly, the downlink stand-alone subframe needs to benewly designated and managed in association with the HARQ process.

Table 5 and Table 6 respectively show a downlink virtual subframe indexand an uplink virtual subframe index on the basis of the frame structureshown in FIG. 9. While the two virtual subframe indexes use “n′”, it isdifferently interpreted for downlink and uplink. Table 5 shows virtualindex values in downlink and Table 6 shows virtual index values inuplink.

TABLE 5 Subframe index (n) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 DLvirtual 0 (UL grant 1 2 3 index (n′) transmision)

TABLE 6 Subframe index (n) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 DLvirtual 0 (UL 1 2 0 (UL index (n′) grant grant trans- trans- mission)mission)

A description will be given using the above-described virtual index n′.The eNB transmits a Un UL grant in a subframe corresponding to adownlink virtual index 0, and the relay receives the Un UL grant. Therelay may transmit uplink data in a subframe corresponding to an uplinkvirtual index 0 in response to the Un UL grant. If retransmissionoccurs, the eNB can transmit an uplink retransmission grant in asubframe corresponding to a downlink virtual index 3 (when it is assumedthat N=3). Uplink retransmission of the relay for the uplink grant isgenerated in a subframe corresponding to an uplink virtual index 3. Thedownlink virtual index 0 indicates a downlink subframe index 0 (i.e.n=0) and the uplink virtual index 0 indicates an uplink subframe index4.

For uplink transmission of the relay in a subframe corresponding to thevirtual index n′, uplink retransmission of the relay is performed in thesubframe corresponding to the virtual index n′+N where N indicates thenumber of Un uplink HARQ processes. More specifically, the eNB maytransmit a retransmission grant for uplink transmission in a subframecorresponding to a downlink virtual index n′+N and the relay may performuplink retransmission in a subframe corresponding to an uplink virtualindex n′+N in response to transmission of the retransmission grant.

When the virtual index is defined and used for only downlink/uplinkpaired subframes of HARQ process, as described above, it is possible tosimply specify a downlink subframe index (or uplink subframe index atwhich retransmission is performed) at which the retransmission index forinitially transmitted data in each uplink backhaul subframe (UL Unsubframe) is received. That is, the HARQ process can be easily managedand used by using the virtual index.

The virtual index n′=0 shown in Table 5 and Table 6 is exemplary, and areference position of virtual index n′=0 may correspond to an integermultiple of a radio frame or radio subframe. Otherwise, n′=0 may be setat an interval of 40 ms (corresponding to four radio frames) inconsideration of an MBSFN signaling period that designates backhaulsubframes.

A scheme of considering a downlink grant stand-alone subframe forasymmetrical backhaul subframe allocation will now be described.

FIG. 10 shows an exemplary frame structure including a downlink grantstand-alone subframe for explaining a HARQ process performed between therelay and the eNB.

As shown in FIG. 10, the scheme illustrated in FIG. 9 is differentlyapplied to the frame structure including a downlink stand-alonesubframe. That is, the processor 175 of the relay needs to determinesubframes having the same HARQ process ID except the downlinkstand-alone subframe, using the number (N) of HARQ processes. That is,the downlink stand-alone subframe among allocated backhaul subframesshould be excluded from indexing.

Referring to FIG. 10, a downlink subframe n+9 is not a downlink backhaulsubframe corresponding to HARQ process ID 0 because it is a downlinkstand-alone subframe. Information about the downlink stand-alonesubframe needs to be signaled to the relay by the eNB through anappropriate method (e.g., through signaling). It may be desirable thatthe eNB signal the information about the downlink stand-alone subframeto the relay using higher layer signaling. Desirably, downlinkstand-alone subframe allocation information is configured by the eNB aspart of downlink subframe allocation signaling and transmitted to therelay at the same timing as downlink subframe allocation signaling.

Virtual subframe indexes are sequentially allocated only to subframesassigned to the backhaul link (Un link). When the downlink stand-alonesubframe exists, as shown in FIG. 10, the virtual subframe indexes canbe defined only for a UL grant and ‘uplink/downlink paired subframes’which are paired according to uplink transmission corresponding to theUL grant. That is, the virtual subframe indexes are not defined for thedownlink stand-alone subframe. However, even when the virtual subframeindexes are not defined, if the UL grant and ‘uplink/downlink pairedsubframes’ which are paired according to uplink transmissioncorresponding to the UL grant include a downlink stand-alone subframe,the HARQ process can be performed by excluding the downlink stand-alonesubframe.

A description will be given of considerations for calculation of thenumber of HARQ processes in association with the aforementioned HARQprocess. The following considerations are applied to calculation of thenumber of HARQ processes in the above-described technique.

The processor 125 of the eNB can determine the number of HARQ processesand the relay can receive information about the number of HARQ processesfrom the eNB. Alternatively, if the relay does not receive theinformation about the number of HARQ processes from the eNB throughsignaling, the processor 175 of the relay may estimate the number ofHARQ processes.

In calculation of the number of HARQ processes, the processor 125 of theeNB needs to exclude subframes that collide with HARQ processes. Forexample, it is necessary to exclude non-MBSFN subframes (e.g. subframeshaving indexes 0, 4, 5 and 9) among backhaul subframes set in a specificpattern or a repeated form of a specific pattern from calculation of thenumber of HARQ processes. If K backhaul subframes among N configuredbackhaul subframes collide with HARQ processes, the processor 125 of theeNB can calculate the number of HARQ processes on the basis of N−K atthe corresponding time. This operation and a series of steps may beperformed by the processor 125 of the eNB or the processor 175 of therelay according to the above-described scheme.

For example, a backhaul subframe allocation information pattern that isrepeated at an interval of 8 ms during a period of 40 ms inevitablycollides (or overlap) with a non-MBSFN subframe allocation pattern thatis repeated at an interval of 10 ms. In this case, it may be desirablethat the processor 125 of the eNB exclude the non-MBSFN subframescorresponding to the non-MBSFN subframe allocation pattern fromcalculation of the number of HARQ processes. As described above, thenumber of HARQ processes is used for the processor 175 of the relay todetermine the HARQ process ID.

The above-mentioned signaling pattern or a bitmap of the eNB may be asignaling pattern or a bitmap pattern which is indexed on the basis ofsubframes or radio frames of the eNB. For example, the bitmap patternmay be indexed on the basis of a subframe having an index 0 in a radioframe, which corresponds to (eNB radio frame index mod 4)=0, or indexedon the basis of a relay subframe index.

If a timing offset exists between the eNB and the relay and the bitmappattern is started at a subframe index 0 of a specific frame of the eNB,the timing offset between the eNB and the relay should be additionallyconsidered in order to calculate subframe indexes corresponding tonon-MBSFN subframes (e.g. subframes corresponding to subframe indexes 0,4, 5 and 9) of the relay from subframe indexes provided for the bitmap.The bitmap pattern can be interpreted in various manners from the pointof view of the relay. One bitmap bit can be considered to indicate onesubframe index or a plurality of subframes.

A description will be given of a method of calculating a subframecapable of being used as a backhaul frame by the processor 175 of therelay using RRC signaling information.

A time-frequency resource for transmission between the eNB and the relayis separately allocated by time-multiplexing transmission between theeNB and the relay and transmission between the relay and the UE.Subframes for transmission between the eNB and the relay are configuredin a higher layer. Transmission from the eNB to the relay is performedin a downlink backhaul subframe and transmission from the relay to theeNB is performed in an uplink backhaul subframe. Subframes configuredfor transmission between the eNB and the relay conform a period of 8 ms.In frame structure type 1, the relay can receive an 8-bit HARQ processindication bitmap [b0 b1 . . . b7] (b0 being the least significant bit(LSGB)). In the eNB cell, the downlink subframe n corresponding to asystem frame number n_(f) is considered to be configured fortransmission between the eNB and the relay if it satisfies the followingtwo conditions.b _(k) is set to 1 for k=(n _(f)*10+n+n _(f,offset)*10+n _(offset))mod8  (1)(n+n _(offset))mod 10 is 1, 2, 3, 6, 7, or 8  (2)

Here, a subframe 0 in a system frame 0 in the eNB cell is synchronizedwith a subframe system n_(f,offset) and subframe n_(offset) in everyrelay cell. If b_(k) is defined in terms of the base subframe index, thedownlink subframe n corresponding to the system frame number n_(f) isconsidered to be configured for transmission between the eNB and therelay if it satisfies the following two conditions.b _(k) is set to 1 for k=(n _(f)*10+n)mod 8  (1)(n+n _(offset))mod 10 is 1, 2, 3, 6, 7, or 8  (2)

Here, n_(offset) may be a negative number or a positive number including0.

To simplify description and implementation, all offset values betweenthe eNB and the relay may be fixed to 0 or a specific value. This fixedoffset value may be defined on a relay group-specific basis. Uplinksubframe allocation corresponding to downlink subframe allocation isdetermined by a predefined offset value. The offset value is 4 generallybut a different value can be applied as the offset value.

A description will be given of a method for calculating a backhaulsubframe available for the HARQ process between the eNB and the relay.

The relay can receive an N-bit (e.g. 8-bit, 10-bit, 20-bit or 40-bit)HARQ process indication bitmap, and then use subframes other thansubframes that cannot be configured by the relay as MBSFN subframes(i.e., non-MBSFM subframes having indexes of 0, 4, 5 and 9, for example)from among backhaul subframes indicated by the bitmap, as backhaulsubframes (Un subframes). The bitmap pattern may be described in termsof the eNB subframe or frame index, or in terms of the relay subframe orframe index, as described above.

If the eNB configures MBSFN subframes in order to provide a multimediabroadcast multicast service (MBMS), or the processor 175 of the relaydecodes an R-PDCCH using a common reference signal (CRC) because the CRCis not present in subframes configured of 3GPP LTE-A dedicated subframesand fake MBSFN subframes, the R-PDCCH cannot be decoded in thecorresponding subframes. Accordingly, it may be desirable to alsoexclude the subframes from calculation of the number of HARQ processesbecause the subframes cannot be used as backhaul subframes. That is,when the eNB signals HARQ related information (e.g., 8-bit bitmap) tothe relay through higher layer signaling, it is necessary to excludesubframes shown in the following table 7 from backhaul subframesindicated by the bitmap in calculation of the number of HARQ processes,as described above.

TABLE 7 Subframes to be excluded from backhaul subframes in HARQ process1 Subframes that cannot be configured as MBSFN subframes in the relaycell (non-MBSFN) 2 Subframes configured for MBMS transmission in the eNBcell 3 3GPP LTE-A dedicated subframes or fake MBSFN subframes

In this manner, HARQ process ID mapping is performed and HARQ processesare operated using subframes other than subframes that cannot be used asbackhaul subframes.

However, in the case of DMRS-based R-PDCCH, it is necessary to excludesubframes shown in Table 8 from calculation of the number of HARQprocesses.

TABLE 8 Subframes to be excluded from backhaul subframes in HARQ process1 Subframes that cannot be configured as MBSFN subframes in the relaycell (non-MBSFN) 2 Subframes configured for MBMS transmission in the eNBcell

Referring to FIG. 8, the 3GPP LTE-A dedicated subframes or fake MBSFNsubframes can be used as backhaul subframes because the 3GPP LTE-Adedicated subframes or fake MBSFN subframes can transmit the DMRS-basedR-PDCCH although the DMRS as well as the CRC do not exist when the eNBperforms MBMS transmission.

The above description can be applied even when the relay has a subframeoffset different from that of the eNB in subframe timing. However, ifthe eNB and the relay have different subframe offsets, the eNB shouldconfigure MBSFN subframes and perform macro UE scheduling inconsideration of the different subframe offsets, and thus the degree offreedom of scheduling may be restricted. Accordingly, it may bedesirable to set the subframe offset to 0.

As described above, the eNB may transmit backhaul subframe allocationinformation to the relay for Un downlink transmission to the relay. Therelay may use, as backhaul subframes (Un subframes), subframes otherthan relay Un downlink non-MBSFN subframes (i.e., subframes that cannotbe used as MBSFN subframes having indexes of 0, 4, 5 and 9, for example)from among received signaling information (e.g., 8-bit bitmap). When theeNB provides true MBSFN service or transmits a positioning RS (PRS), theabove subframes cannot be used as backhaul subframes.

FIG. 11 illustrates MBSFN configurations for interference coordination.FIG. 11 a shows interference measurement in a PDSCH region and FIG. 11 bshows interference measurement in a second slot.

If the eNB attempts to perform coordination such as interferencecoordination with other cell, the eNB needs to signal the followingadditional information to the relay. For example, a macro eNB (or cell)can configure MBSFN subframes, as shown in FIGS. 11( a) and 11(b), toreduce interference in a measurement RE of a pico cell such that thepico cell can perform reduced-interference data transmission. A similaroperation can be performed using an almost blank subframe (ABS). A CRSsignaled by a network for measurement is received through the PDSCHregion of the pico cell in the case of FIG. 11( a), whereas the CRS isreceived through the second slot in the case of FIG. 11( b).

While interference coordination information using MBSFN or ABS is notconsidered because the nature of the interference coordinationinformation is different from the backhaul subframe allocationinformation, the eNB can efficiently combine the interferencecoordination information and the backhaul subframe allocationinformation and transmit the combined information to the relay asinter-cell interference coordination (ICIC) becomes applicable to therelay. The processor 175 of the relay needs to determine how to operateby receiving the information even if the information is not the combinedinformation (signal).

There is a method of configuring Un subframe allocation bitmapinformation using subframe information that cannot be allocated to Unsubframes. It may be possible to configure a signal by adding subframes,which cannot be used as Un subframes because they are MBSFN subframes orABSs, to the Un subframe allocation bitmap information. That is, therelay can recognize Un subframe allocation information from combinedsignaling information. In addition, since CRS transmission is notperformed in the case of LTE-A dedicated subframes, a CRS-based relaycannot use the LTE-A dedicated subframes as Un subframes. Accordingly,the CRS-based relay needs to exclude the LTE-A subframes from Unsubframes and perform HARQ process. The eNB can signal the LTE-Adedicated subframes to the relay through separate signaling, as shown inTable 9.

TABLE 9 Examples of signaling types for signaling LTE-A dedicatedsubframe information 1 Un subframe allocation signaling 2 Coordinationsignaling (e.g. MBSFN or ABS for enhanced inter-cell interferencecoordination (eICIC) or measurement) 3 LTE-A dedicatedsubframe(including no CRS) 4 True MBSFN subframe (MCH) 5 Positioning RSsubframe (including no data transmission) 6 Combination of signalinginformation 1 to 5.

The signaling information shown in Table 9 may be signaled in differentforms by being combined. Particularly, combination of signalinginformation 1 and 2 can reduce signaling overhead. If the signalinginformation 1 and 2 is configured in the form of a bitmap, a compactsignal can be configured by obtaining the union or intersection of thetwo bitmaps or by masking the two bitmaps. Signaling information 3 maybe combined with the signaling information 1 and 2. The signalinginformation 3 can be signal by the eNB to a CRS-based relay. A relayneeds to differently interpret signaling according to whether the relayis based on CRS or DMRS.

When the Un subframe allocation bitmap is 8 bits and an interferencesubframe bitmap is 40 bits, the processor 175 of the relay can configure40 bits by a concatenation of 8-bit units, consider subframes other thannon-MBSFN subframes, true MBSFN subframes and interference coordinationsubframes as allocated Un subframes, and perform HARQ operation in theUn subframes. A relay that decodes an R-PDCCH based on the CRS needs toperform a HARQ process by excluding a subframe including no CRS frombackhaul subframes. While a subframe that cannot be used as a Unsubframe is generally excluded from HARQ process mapping, it may beconsidered to suspend HARQ operation in the corresponding subframewithout excluding the subframe from HARQ process mapping if the subframeis not frequently generated. This method determines Un subframesaccording to frequency of generation of subframes rather than signalingtype. Accordingly, different Un subframe determination methods can beimplemented for relays.

Table 10 shows backhaul subframe information and unavailable subframeinformation.

TABLE 10 subframe index (SF index) 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 89 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 Fake X X X X X X X X X X X X XX X MBSFN (Relay) 8 ms 0 1 1 1 0 0 1 1 0 1 1 1 0 0 1 1 0 1 1 1 0 0 1 1 01 1 1 0 0 1 1 0 1 1 1 0 0 1 1 Bitmap (1: Un SF) 40 ms 1 1 1 1 1 bitmap(eICIC) True 1 MBSFN (eNB) LTE-A 1 1 1 1 1 (eNB) Available Un-SF 1 1 1 11 1 1 1 1 1 (1: Un SF)

Referring to FIG. 10, the eNB can signal Fake MBSFN subframe allocationinformation (corresponding to subframe indexes represented by X) to therelay. In addition, the eNB can signal backhaul subframe (Un subframe)allocation information in the form of an 8-bit bitmap (corresponding tosubframes signaled by ‘1’ to the relay). Furthermore, the eNB cantransmit interference coordination subframe allocation information in a40-bit bitmap pattern (corresponding to subframes signaled by ‘1’) tothe relay. And, the eNB can transmit true MBSFN subframe allocationinformation and LTE-A dedicated subframe allocation information(corresponding to subframes signaled by ‘1’) to the relay. Accordingly,the processor 175 of the relay can recognize, as available backhaulsubframes, subframes other than the fake MBSFN subframes, interferencecoordination subframes, true MBSFN subframes and LTE-A dedicatedsubframes from among the subframes allocated as backhaul subframes (Unsubframes). Otherwise, the eNB can directly signal available backhaulsubframes to the relay such that the relay can be aware of the availablebackhaul subframe information.

Table 11 shows the information shown in Table 100 as a unified signal.

TABLE 11 Subframe index (SF index) 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 89 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 8 ms 1 0 0 0 1 1 0 0 1 0 0 0 11 0 0 1 0 0 0 1 1 0 0 1 0 0 0 1 1 0 0 1 0 0 0 1 1 0 0 Bitmap (0: Un SF)40 ms bitmap 1 1 1 1 1 (eICIC) True 1 MBSFN (eNB) LTE-A 1 1 1 1 1 (eNB)Colum-wise sum 2 0 1 1 1 1 0 0 2 0 1 0 1 1 0 0 2 0 1 0 1 1 0 0 2 0 1 0 11 0 0 2 0 1 0 1 1 0 0 of each bit Unified 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00 0 0 0 signaling pattern (0: Un SF) Relay can receive unified signalingpattern and configure backhaul (Un) HARQ operation based on subframesother than the next fake MBSFN subframe. Fake MBSFN X X X X X X X X X XX X X X X (RN) Available 0 0 0 0 0 0 0 0 0 0 backhaul ubframe (Un SF)(0: Un SF)

Referring to FIG. 11, it is assumed that the eNB transmits the Unsubframe allocation information in the form of an 8-bit bitmap to therelay and transmits a 40-bit interference coordination informationbitmap to the relay. This assumption is applicable to a bitmap of othersignaling information, which has a different pattern length.

The eNB normally transmits the 8-bit bitmap pattern. In this case, theeNB may determine a final signal, that is, a 40-bit bitmap pattern, byconsidering the 40-bit interference coordination information bitmap(including interference coordination subframe information) and a 40-bitbitmap pattern corresponding to five repeated 8-bit Un subframe bitmaps,together. Accordingly, it is possible to determine Un subframes usingonly the interference coordination information bitmap pattern withoutthe Un subframe bitmap pattern.

It is also possible to reflect all signaling information shown in Table10 in the coordination bitmap pattern to obtain a unified bitmap andtransmit the unified bitmap. An agreement should be made between the eNBand the relay in advance such that the relay can interpret the unifiedbitmap. The unified bitmap can be unified as a signal other than acoordination signal.

The eNB can transmit available backhaul subframe allocation informationin the unified signaling pattern shown in Table 11 to the relay suchthat the relay can perform a HARQ process. In the unified signalingpattern shown in Table 11, subframes represented by ‘0’ correspond tobackhaul subframes in which the relay performs the HARQ process. The eNBmay transmit the unified signaling pattern, subframes allocated asbackhaul subframes (Un subframes), interference coordination subframes,true MBSFN subframes and LTE-A dedicated subframes together throughindependent signaling processes. In this case, the relay may use thesubframes to verify whether the subframes are available Un subframes.

When the relay receives the backhaul subframes (Un subframes),interference coordination subframes, true MBSFN subframes, and LTE-Adedicated subframes from the eNB through independent signaling processesor a unified signaling process, the processor 175 of the relay candetermine subframes, which are left after excluding fake MBSFN subframesfrom the received subframes, as available backhaul subframes. Theprocessor 175 of the relay can perform backhaul HARQ process using thedetermined available backhaul subframes. The processor 175 of the relaycan determine the backhaul subframes by combining independent signalinginformation or on the basis of the received unified signalinginformation. The backhaul subframes may correspond to subframesrepresented by ‘0’ in the unified signaling pattern shown in FIG. 11.

While the HARQ process and signaling method focus on the eNB and therelay, the relay is an exemplary entity of a wireless communication an dthe HARQ process and signaling method can be applied to other entities.

The signaling processes and operations related to Table 10 and Table 11are not defined only for one-direction communication from the eNB to therelay, and they can be applied to bi-direction communication between twocells if the cells are considered to be equal.

Table 12 shows system information block (SIB) type 2 of the 3GPP LTEsystem.

TABLE 12 SystemInformationBlockType2 information element -- ASN1STARTSystemInformationBlockType2 ::= SEQUENCE {   ac-BarringInfo   SEQUENCE {    ac-BarringForEmergency     BOOLEAN,     ac-BarringForMO-Signalling    AC-BarringConfig OPTIONAL,  -- Need OP     ac-BarringForMO-Data    AC-BarringConfig OPTIONAL  -- Need OP   } OPTIONAL,  -- Need OP  radioResourceConfigCommon   RadioResourceConfigCommonSIB,  ue-TimersAndConstants   UE-TimersAndConstants,   freqInfo   SEQUENCE {    ul-CarrierFreq     ARFCN-ValueEUTRA OPTIONAL,  -- Need OP    ul-Bandwidth     ENUMERATED {n6, n15, n25, n50, n75, n100}OPTIONAL,  -- Need OP     additionalSpectrumEmission    AdditionalSpectrumEmission   },   mbsfn-SubframeConfigList  MBSFN-SubframeConfigList OPTIONAL,  -- Need OR  timeAlignmentTimerCommon TimeAlignmentTimer,   ... } AC-BarringConfig::= SEQUENCE {   ac-BarringFactor   ENUMERATED {     p00, p05, p10, p15,p20, p25, p30, p40,     p50, p60, p70, p75, p80, p85, p90, p95},  ac-BarringTime   ENUMERATED {s4, s8, s16, s32, s64, s128, s256, s512},  ac-BarringForSpecialAC   BIT STRING (SIZE(5)) }MBSFN-SubframeConfigList ::= SEQUENCE (SIZE (1..maxMBSFN-Allocations))OF MBSFN-SubframeConfig MBSFN-SubframeConfig ::= SEQUENCE {  radioframeAllocationPeriod   ENUMERATED {n1, n2, n4, n8, n16, n32},  radioframeAllocationOffset   INTEGER (0..7),   subframeAllocation  CHOICE {     oneFrame     BIT STRING (SIZE(6)),     fourFrames     BITSTRING (SIZE(24))   } } -- ASN1STOP

Referring to FIG. 12, SIB type 2 information may include MBSFN subframeconfiguration list information. According to the MBSFN subframeconfiguration list information, a subframe pattern can be determined byradioframeAllocationPeriod, radioframeAllocationOffset,subframeAllocation (oneFrame, fourFrames). As many subframe patterns asthe number of maxMBSFN-Allocations can be designated.

FIGS. 12 and 13 illustrate exemplary MBSFN subframe configurations.

These configurations are equally used to configure fake-MBSFN.Accordingly, it may be desirable to exclude subframes to be used as trueMBSFN subframes and fake-MBSFN subframes from a bitmap pattern used forbackhaul subframe allocation. Since the backhaul subframe pattern, whichcorresponds to repeated N-bit bitmap patterns, and the MBSFN bitmappattern having a period different from that of the backhaul subframepattern are unrelated independent patterns, an available backhaulsubframe bitmap exhibits a very irregular pattern when the MBSFN bitmappattern is excluded from the backhaul subframe bitmap. Particularly, ifthe eNB covers eight MBSFN areas as shown in FIG. 12, the number ofsubframes set to MBSFN subframes increases. In this case, an input valuerange needs to be set when [Equation 16] is applied to determine thenumber of HARQ processes and HARQ process ID.

$\begin{matrix}{N_{HARQ} = {\max\limits_{i = {0\mspace{11mu}\ldots\mspace{14mu} N}}{\sum\limits_{j = i}^{i + 8}\left\{ \begin{matrix}1 & {{Un}\mspace{14mu}{subframe}} \\0 & {{Uu}\mspace{14mu}{subframe}}\end{matrix} \right.}}} & \left\lbrack {{Equation}\mspace{14mu} 16} \right\rbrack\end{matrix}$

Where, N denotes an RRC-signaled 10 ms or 40 ms Un subframeconfiguration period.

The number of HARQ processes and a minimum WIT depend on an input value.As a method of setting the input value range, a subframe section(window) in which a maximum number of available backhaul subframes canbe obtained, from a result obtained by masking out the MBSFN subframebitmap pattern from the Un subframe bitmap pattern, is used as an inputparameter. This can minimize the HARQ minimum RTT in backhaul subframes.Alternatively, a subframe section (window) in which a minimum number ofavailable backhaul subframes can be obtained, from the result obtainedby masking out the MBSFN subframe bitmap pattern from the Un subframebitmap pattern, is used as an input parameter. This can solve a problemcaused by suspending with respect to MBSFN subframes while increasingthe HARQ minimum RTT in the backhaul subframes. Alternatively, K (aformula input parameter size) subframes from a specific position(obtained by calculation or predetermined) in MBSFN subframes can beselected and used. In this case, a value (e.g., average) that does notexceed a specific critical point in consideration of the predeterminednumber of times of suspending and other system parameters can be used asan input parameter.

In the aforementioned method for determining available effectivebackhaul subframes, the effective backhaul subframes are determined byadditionally taking the following into account. Two types of bitmappatterns exist as a signal transmitted/received for eICIC according tousage and characteristics thereof, and each bitmap pattern may indicatea specific subframe. Especially, each bitmap pattern can be used todesignate an ABS pattern. For example, the bitmap patterns have a periodof 40 ms in the case of FDD and 20 ms (configurations 1 to 5), e.g., 70ms (configuration 0) and 60 ms (configuration 6) in the case of TDD. Itis assumed that the bitmap patterns are semi-statically updated and thefrequency of update of the bitmap patterns is lower than the frequencyof update of 3GPP LTE Release 8/9 RNTP signal.

If the two types of bitmap patterns are respectively referred to asbitmap 1 and bitmap 2, they can be defined as follows. Bitmap 1 mayindicate subframes corresponding to ABSs and bitmap 2 may indicate asub-set of the subframes indicated by bitmap 1. Bitmap 2 is recommendedin a reception mode for configuration of limited radio link monitoring(RLM)/RRM measurement. A serving cell can indicate actual resources forRLM/RRM and CSI through RRC signaling. Bitmap 2 can be triggerednon-periodically or on an event basis.

Since ABSs designated by the bitmap patterns cannot be used as backhaulsubframes, it may be desirable to exclude the ABSs from availableeffective backhaul subframes. A bitmap to be excluded may be determinedas follows since the bitmaps 1 and 2 have different usages. Subframesindicated by bitmap 1 may be excluded from the effective backhaulsubframes. Otherwise, subframes indicated by bitmap 2 may be excludedfrom the effective backhaul subframes. Alternatively, subframesindicated by a pattern corresponding to the union of bitmap 1 and bitmap2 (e.g., subframes indicated by bitmap 1) may be excluded from theeffective backhaul subframes.

The eNB and the relay can perform efficient HARQ process through thebackhaul link according to the above-mentioned method for determiningthe number of HARQ processes and the method for signaling the number ofHARQ processes. The method for determining the number of HARQ processesand the method for signaling the number of HARQ processes can be appliedto a link between the eNB and the UE and a link between the relay andthe UE as well as the link between the eNB and the relay.

The embodiments described above are combinations of elements andfeatures of the present invention. The elements or features may beconsidered selective unless otherwise mentioned. Each element or featuremay be practiced without being combined with other elements or features.Further, an embodiment of the present invention may be constructed bycombining parts of the elements and/or features. Operation ordersdescribed in embodiments of the present invention may be rearranged.Some constructions of any one embodiment may be included in anotherembodiment and may be replaced with corresponding constructions ofanother embodiment. It is obvious to those skilled in the art thatclaims that are not explicitly cited in each other in the appendedclaims may be presented in combination as an exemplary embodiment of thepresent invention or included as a new claim by a subsequent amendmentafter the application is filed.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein.

INDUSTRIAL APPLICABILITY

The method for performing a HARQ process and the apparatus using thesame are applicable to a variety of communication systems including 3GPPLTE, LTE-A systems, etc.

The invention claimed is:
 1. A method of performing a hybrid automaticrepeat request (HARQ) process operation using a frequency divisionduplex (FDD) frame structure by a base station (BS) in a wirelesscommunication system, the method comprising: transmitting informationregarding a number of HARQ processes between the BS and a relay node(RN) to the RN, wherein the number of the HARQ processes depends on atleast one subframe configured for transmission between the BS and theRN, wherein each of the HARQ processes is assigned to at least onesubframe configured for RN-to-BS transmission according to the number ofthe HARQ processes, and wherein the at least one subframe to which eachof the HARQ processes is assigned must be a multicast broadcast singlefrequency network (MBSFN) subframe.
 2. The method of claim 1, whereinthe information is transmitted as a type of 8-bit bitmap.
 3. The methodof claim 2, wherein the number of the HARQ processes is determined bydecimal equivalent of the binary number representing the 8-bit bitmap.4. The method of claim 2, wherein the number of the HARQ processescorresponds to a number of bit represented by “1” among at least onebinary number representing the 8-bit bitmap.
 5. The method of claim 1,wherein the information is transmitted through a higher layer signaling.6. The method of claim 1, wherein the information is transmitted througha higher layer signaling.
 7. The method of claim 1, wherein the at leastone subframe to which each of the HARQ processes is assigned correspondsto subframe indexes 0, 4, 5, or
 9. 8. A method of performing a hybridautomatic repeat request (HARQ) process operation using a frequencydivision duplex (FDD) frame structure at a relay node (RN) in a wirelesscommunication system, the method comprising: receiving informationregarding a number of HARQ processes between a base station (BS) and theRN from the BS, wherein the number of the HARQ processes depends on atleast one subframe configured for transmission between the BS and theRN, wherein each of the HARQ processes is assigned to at least onesubframe configured for RN-to-BS transmission according to the number ofthe HARQ processes, and wherein the at least one subframe to which eachof the HARQ processes is assigned must be a multicast broadcast singlefrequency network (MBSFN) subframe.
 9. The method of claim 8, whereinthe information is received as a type of 8-bit bitmap.
 10. The method ofclaim 9, wherein the number of the HARQ processes is determined bydecimal equivalent of the binary number representing the 8-bit bitmap.11. The method of claim 9, wherein the number of the HARQ processescorresponds to a number of bit represented by “1” among at least onebinary number representing the 8-bit bitmap.
 12. The method of claim 8,wherein the information is received through a higher layer signaling.13. The method of claim 8, wherein the at least one subframe to whicheach of the HARQ processes is assigned corresponds to subframe indexes0, 4, 5, or
 9. 14. A base station (BS) of performing a hybrid automaticrepeat request (HARQ) process operation using a frequency divisionduplex (FDD) frame structure in a wireless communication system, the BScomprising: a transmitter configured to transmit information regarding anumber of HARQ processes between the BS and a relay node (RN) to the RN,wherein the number of the HARQ processes depends on at least onesubframe configured for transmission between the BS and the RN, whereineach of the HARQ processes is assigned to at least one subframeconfigured for RN-to-BS transmission according to the number of the HARQprocesses, and wherein the at least one subframe to which each of theHARQ processes is assigned must be a multicast broadcast singlefrequency network (MBSFN) subframe.
 15. The BS of claim 14, wherein theinformation is transmitted as a type of 8-bit bitmap.
 16. The BS ofclaim 14, wherein the number of the HARQ processes is determined bydecimal equivalent of the binary number representing the 8-bit bitmap.17. The BS of claim 16, wherein the number of the HARQ processescorresponds to a number of bits represented by “1” among at least onebinary number representing the 8-bit bitmap.
 18. The BS of claim 14,wherein the at least one subframe to which each of the HARQ processes isassigned corresponds to subframe indexes 0, 4, 5, or
 9. 19. A relay node(RN) of performing a hybrid automatic repeat request (HARQ) processoperation using a frequency division duplex (FDD) frame structure at arelay node (RN) in a wireless communication system, the RN comprising: areceiver configured to receive information regarding a number of HARQprocesses between a base station (BS) and the RN from the BS; aprocessor configured to acquire the number of the HARQ processes,wherein the number of the HARQ processes depends on at least onesubframe configured for transmission between the BS and the RN, whereineach of the HARQ processes is assigned to at least one subframeconfigured for RN-to-BS transmission according to the number of the HARQprocesses, and wherein the at least one subframe to which each of theHARQ processes is assigned must be a multicast broadcast singlefrequency network (MBSFN) subframe.
 20. The RN of claim 19, wherein theat least one subframe to which each of the HARQ processes is assignedcorresponds to subframe indexes 0, 4, 5, or 9.